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Current Cost Support Forum • View topic - Lost Data on a larger system?

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Forum locked This topic is locked, you cannot edit posts or make further replies.  [ 23 posts ]  Go to page 1, 2, 3  Next
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PostPosted: Mon Sep 19, 2011 12:33 pm 
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Location: Cambridge, England
I have a system consisting of a whole house sensor, three mini transmitters, and a single IAM.

I'm noticing that I'm losing approximately 10%-20% of my data at the base unit, and I believe this is caused by collisions on transmission. I'm guessing you're using the Zigbee protocol given you have the badge on your website.

How are collisions resolved on the transmitters? Does the system try to minimize them or is it just random?
What baud rate do the sensors transmit to the base station at? Is there actually enough bandwidth for 10 sensors?

I thought I posted a message about this here yesterday, but it seems that I must have closed the window before posting, as it's not here any longer.


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PostPosted: Mon Sep 19, 2011 1:11 pm 
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Location: East Sussex
I think only their next generation of products will use the Zigbee.

The current ones on offer only transmit and no handshake takes place to resend lost or corrupt data :(

I would also guess other gadget that may be in the home could also cause data loss.

Automan.


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PostPosted: Mon Sep 19, 2011 2:46 pm 
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PostPosted: Tue Sep 20, 2011 1:56 pm 
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Thanks for the replies guys.

I don't think it's inherently a problem with the PC processing the message, as the RS232 will just transmit the data. There isn't any handshaking as far as I can tell.

Also, we still don't know what the over the air baud rate is. PC may be 57600, but there's no reason to expect the transmitters work at that speed. If they worked at a higher baud rate, there'd be less chance of a collision. Flip side of course is that if they're actually slower, there's more chance.


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PostPosted: Fri Sep 23, 2011 12:17 am 
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PostPosted: Sat Sep 24, 2011 5:35 pm 
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Location: Melbourne, Australia

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PostPosted: Sun Sep 25, 2011 5:40 pm 
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Seeker, sorry if my mention of your system's data rates above was confusing/ or wrong & thanks for the analysis, but guess I missed your overall conclusion and a comment on what the previous emailer was saying about the (v low!) baud rates over air. Guess no-one (probably including most of the cc guys) knows how envi really works!.

qs
1) why does the addition of the extra data cause your solar data/hr to be (consistently) different from the house data and much lower that w/o the extra data?

2) what's the likely answer to the original q - ie would envi support 10 sensors, in a usable fashion?

3) A practical q:- given the way that the data rates reduce with additional sensor lines, what is the correct/best/most accurate way to calculate the power for a sensor from the live sensor readings. Is it still, as cc recommend, to multiply the sensor reading in xml by the interval in secs since last reading, bearing in mind that maybe readings are lost between clamp/transmitter (by collisions) and pc, or is it better add up the readings and to scale according to the average no of readings received in an hour somehow? Or what.

John


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PostPosted: Mon Sep 26, 2011 5:13 am 
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PostPosted: Mon Sep 26, 2011 1:49 pm 
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3) A practical q:- given the way that the data rates reduce with additional sensor lines, what is the correct/best/most accurate way to calculate the power for a sensor from the live sensor readings. Is it still, as cc recommend, to multiply the sensor reading in xml by the interval in secs since last reading, bearing in mind that maybe readings are lost between clamp/transmitter (by collisions) and pc, or is it better add up the readings and to scale according to the average no of readings received in an hour somehow? Or what. [/quote]
Well this is the crux of it. Usability depends on the Mission. So if I want an estimate of Energy used each hour or 30 minutes, a single sample in each minute will probably suffice (This is what Techtonic Energy Station does). Assuming the samples are normally distributed a sample of 30 will give an approximation of the mean +/- 2SD ie about 99.5% confidence. (N.B. If you average the 6 second readings in each minute you can be certain that it is normally distributed).
On the other hand, if my mission is to identify appliances in use at any particular time I would need to pattern match the instantaneous power at a high frequency. so 6 second intervals is probably the outside of what is acceptable. (Doesn't negate the approach, but reduces confidence in result).

Wow! that was a bit esoteric wasn't it? :roll: I didn't delete it cos I put a lot of thought into it :ugeek:.
In practical terms the difference in the average value between your two approaches is marginal though the second approach is likely to have more variance.
In my home-brew system reading the inverter (CC not involved), i read the inverter each minute multiply the average reading before and after the interval by the interval length and sum over 10 minutes. I have special handling if I miss a reading on the minute boundary.

No not too esoteric at all imo - to quote the great man 'as simple as possible, but not simpler'. I'm always pleased to see someone quoting the 'central limit' theory - one of the most amazing theories in stats IMO.

My 'mission' in live_sol is to do the best estimate for a house with solar, of the power saved and 'wasted' (ie going back to grid at 0 credit) wrt the user, and to get the best estimate of the billable power each day.

The system is non linear because of the threshold effect ie if solar-house > 0 then some saving & waste else saving only, so I concluded that I need to do the calc in realtime every 6 (or so secs) to get best estimates and potentially just sampling might be a good deal less accurate imo. Of course there are still errors, only some of which cancel via averaging, eg the time is only to nearest sec, plus PF & clamp errors, potential data losses as above, and of course we are doing the difference of nos with errors hence some error magnification. Given all of this, and with testing I've done vs my meter (SteveH has also done these, and I hope to do them on your data too soon), I'm mostly getting the billable power estimate to within (+ or -) < 5kwh + about (+ or -) <5% in my house power of 15-20kwh per day, so not too bad, and better than is reported many others using other apps...but I'd like to improve it if possible, so all ideas welcome.

John


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PostPosted: Tue Sep 27, 2011 4:35 am 
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